Oxidative dyeing, otherwise known as permanent colouring leads to irreversible physico-chemical changes to the hair. Typically, during this process, two components are mixed together prior to application to the hair. These components usually comprise an oxidising agent, such as hydrogen peroxide, and a dyeing material, such as oxidative dye precursors and couplers (buffered at a high pH, typically around 10). After contacting with the hair, the mixture is left for a period of time suitable to allow the required colour transformation to occur, after which the hair becomes more hydrophilic versus non-coloured hair due to irreversible chemical changes. While not wishing to be bound by theory, this change in hair hydrophilicity appears to be due, among other things, to the oxidation of the keratin-keratin cysteine amino acids within the hair creating more hydrophilic cysteic acid amino acid residues and the hydrolysis of the hair's natural hydrophobic, protective layer denoted as the F-Layer, a covalently attached lipid to the outer epicuticular envelope, 18-methyleicosanoic acid. This colouring process is usually repeated regularly by consumers in order to maintain their desired hair colour and colour intensity and also to ensure that new hair growth has the same colour as the older hair. As a consequence the hair changes polarity from a relatively hydrophobic surface near the scalp where it could be experiencing its first colour, to a progressively more polar substrate at the hair tips, which may have been subjected to multiple colouring treatments. A discussion of oxidation dyeing of hair can be found in “The Science of Hair Care” by Charles Zviak, Marcel Dekker, New York, 1986. These irreversible physicochemical changes can manifest themselves as increased roughness, brittleness and dryness leading to less manageable hair.
After the colouring process human hair becomes soiled due to its contact with the surrounding environment and from the sebum secreted by the scalp. This soiling of the hair causes it to have a dirty feel and unattractive appearance and necessitates shampooing with frequent regularity. Shampooing cleans the hair by removing excess soil and sebum, but can leave the hair in a wet, tangled, and generally unmanageable state. Once the hair dries, it is often left in a dry, rough, lustreless, or frizzy condition due to the removal of the hair's natural oils and other natural or deposited conditioning and moisturizing components. Hair can also be left with increased levels of static upon drying which can interfere with combing and result in a condition commonly referred to as “fly-away-hair”. These conditions tend to be exaggerated on hair which has been previously oxidatively coloured.
It is known to use hair conditioners to alleviate the above problems. More specifically, it is known to add conditioning materials to colorant products or to supply them separately as part of colorant kits. It is also known to use conditioners in the shampooing process. These approaches range from post-shampoo application of hair conditioners such as leave-on or rinse-off products, to hair conditioning shampoos which attempt to both cleanse and condition the hair from a single product. Hair conditioners are typically applied in a separate step following shampooing. The hair conditioners are either rinsed-off or left-on, depending upon the type of product used. Polydimethylsiloxanes (PDMS) are often employed as conditioning materials to improve hair feel. However, it is known that, in the case of more hydrophilic hair obtained after oxidative coloring, PDMS deposition is greatly reduced, and cannot provide the same benefit in hair condition as for non-oxidatively colored hair. Moreover, PDMS based conditioners are not retained on the hair for a sufficient period of time for the benefit to be durable.
The use of more polar silicones, such as amino-functionalized silicones, and even more hydrophilic quat-functionalized silicones is known—reference is made to EP 0 275 707 and WO 99/49836 on the one hand and U.S. Pat. No. 6,136,304 on the other. However, whereas these exhibit improved deposition onto the more polar damaged hair, their durability on such substrates is poor—the increased polarity renders these silicones more susceptible to removal via washing (thereby reducing durability). Without wishing to be bound by theory, this is believed to result from such silicones having increased aqueous affinity versus the less polar silicones making them more apt to being washed away during shampooing.
The addition of organomodified resins to non-polar polydimethylsiloxanes is known. In WO 92/10161, PDMS-based silicone conditioners are modified by addition of a resin, in that case to improve silicone deposition onto undamaged hair. However, this does not address the issue of durability onto chemically damaged hair: polydimethylsiloxanes are too non-polar for sufficient deposition onto the hydrophilic, chemically damaged hair for even an initial conditioning benefit to be achieved, let alone a durable benefit.
Organomodified siloxane resins have also been added to the very hydrophilic silicone copolyols. US 2001/0043912 is concerned with tackling the problem of “frizzy” hair and proposes to modify dimethicone copolyols by addition of a silicone resin to achieve this aim. This document is not concerned with improving conditioner durability. Moreover, the compositions proposed would not achieve that aim either, since even the resin-modified dimethicone copolyols are far too hydrophilic (100 on the Hydrophilicity Index, detailed below), so would be washed off during any washing step immediately subsequent to application.
With the above discussion in mind, the invention will ideally provide a hair treatment composition comprising a conditioning agent that is durable, i.e. does not wash off so rapidly that the conditioning benefit is lost to the consumer, especially on chemically damaged hair, such as occurs during permanent dyeing, bleaching and permanent waving.